Threat Intelligence / CVE / CVE-2026-40403

CVE-2026-40403 — Microsoft Windows 10 Version 1607

CVSS v3.1 8.8 (HIGH) · EPSS 0.0% (higher than 4.5% of all scored CVEs) · Priority 4.6/10 · Published 2026-05-12

As of 2026-05-26, CVE-2026-40403 is a HIGH-severity vulnerability in Microsoft Windows 10 Version 1607, CVSS v3.1 8.8, EPSS 0.0% (4.5th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-40403, most recently “Microsoft May 2026 Patch Tuesday — 137 CVEs, 31 Critical (16 RCE) Including CVE-2026-41089 Pre-Auth Netlogon Stack Overflow on Domain Controllers”.

Last updated: 2026-05-26

What is CVE-2026-40403?

Heap-based buffer overflow in Windows Win32K - GRFX allows an authorized attacker to execute code locally.

The record classifies CVE-2026-40403 under weakness class CWE-122. Its CVSS v3 base vector states that the flaw requires local access to the host, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 10 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 123 days ago.

Severity and exploitation probability

CVSS v3.1 base score
8.8 — HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C
EPSS (FIRST)
0.0% probability of exploitation in the next 30 days, higher than 4.5% of all scored CVEs
CISA KEV
Not listed in the CISA Known Exploited Vulnerabilities catalog
Threadlinqs priority
4.6/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
Published
2026-05-12, last modified 2026-05-26

Is CVE-2026-40403 being exploited?

It currently carries a trending score of 6 in the Threadlinqs vulnerability feed.

Affected products and versions

How to fix CVE-2026-40403

No vendor patch reference has been recorded for CVE-2026-40403 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

Threat activity tracking CVE-2026-40403

1 tracked threat in the Threadlinqs corpus references CVE-2026-40403, either in the campaign’s CVE list or as an indicator on the campaign record.

Sources

Seeded from cveorg and not yet processed by the Threadlinqs enrichment pipeline, so blank CVSS, EPSS or KEV fields above mean NOT MEASURED rather than measured-absent.

Full detection coverage & IOCs for threats exploiting CVE-2026-40403 are available via the Threadlinqs MCP server (Purple tier). View plans →

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